66 EDMUND B. WILSON 



the three small chromosomes are still easily seen in many of the 

 nuclei; but they are now pale and diffuse like the bivalents. In 

 this respect the third small chromosome differs from a " super- 

 numerary" of the type described in my former paper, and agrees 

 exactly with the m-chromosomes. 



Each nucleus contains at this period a single compact, rounded 

 and* intensely staining chromatic nucleolus, which is no doubt 

 the odd or accessory chromosome (monosome), as in so many 

 other forms, 4 and in addition there is present a conspicuous, rounded 



4 This identification is in agreement with that of most observers in recent years. 

 A few writers have however disputed the view that the chromatic nucleolus of 

 the growth period of the spermatocytes is a chromosome e. g., Moore and 

 Robinson in case of the cockroach ('05), Foot and Strobell in the case of Anasa('07) 

 and Euschistus ('09), and Arnold ('08), in case of Hydrophilus. The results of 

 Moore and Robinson on this point are opposed by those of Stevens ('05),Wassilieff 

 ('07), and more particularly by the detailed observations of Morse ('09). Those 

 of Foot and Strobell on Anasa are not sustained by the later ones of Lefevre and 

 McGill ('08). Among others who have in the past two years adhered to the view 

 here adopted may be mentioned Otte ('07), Davis ('08), Boring ('07), Jordan ('08), 

 Stevens ('08, '09), McClung ('08), Robertson ('08), Randolph ('08), Nowlin ('08), 

 Payne ('09,) Wilson ('096, '09c), Gutherz ('09), Wallace ('09), Gerard ('09), and 

 Buchner ('09a). Since I intend to return to the subject hereafter I will take this 

 occasion for only brief comment on some of these results, without attempting a 

 full review of the literature. 



Moore and Robinson, who have been followed by Arnold (Strasburger, '07, '09. 

 expresses the same opinion) also regard the body that is seen passing to one pole in 

 one of the maturation divisions ("accessory chromosome") as not a chromosome 

 but a ' 'nucleolus." I find it incredible that anyone can hold to such a view who 

 reckons squarely with the large existing body of direct and detailed observation 

 upon the accessory chromosome itself; and this view seems to be quite ruled out of 

 court by comparative studies on the sex-chromosomes, such for instance as those 

 of Payne on Gelastocoris and the reduvioids. I will not enter here upon the maze 

 of difficulties regarding the numerical relations of the chromosomes which the 

 same view involves, since they have already been indicated by Gutherz ('09), in a 

 recent reply to Strasburger. My own preparations, including an extensive series 

 of sections and smears especially of Protenor, Lygaeus and Pyrrhocoris leave in 

 my mind not the least doubt of the identity of the chromatin-(chromosome)- 

 nucleolus of the growth period with the odd chromosome (monosome) of the 

 spermatogonia, and with the heterotropic or accessory chromosome of the mat- 

 uration-divisions. 



Certain writers have seemed to take it for granted that the accessory chromosome 

 or "monosome" is always characterized by its nucleolus-like condition in the rest- 

 ing nuclei, not only in the spermatocytes but also in the spermatogonial and other 



